Anhydrous magnesium chloride, commonly used as a support in high activity olefin polymerization catalyst is, often not, convenient because it is very brittle and undergoes easy attrition in the polymerization reactor. Silica is a well known support for fluidized bed gas phase polymerization of olefins using titanium based Ziegler-Natta catalysts. However, when used with metallocene type catalysts silica supports show low polymerization activities. Therefore, a combination of the two, namely, silica and anhydrous magnesium chloride, offers a good balance of properties to prepare catalysts with high activity, controlled particle size and good resistance to attrition.
Olefin polymerization and copolymerization catalysts comprising a metallocene and an aluminum alkyl component are well known in the prior art. The molecular weight of the polymer can be controlled by adjusting the reaction temperature or the amount of co-catalyst or by the addition of hydrogen. The metallocene catalysts require the use of methylaluminoxane (herein after referred to as MAO) as co-catalyst, which is produced by reacting an aluminum alkyl with water.